Remove some dead code (#6611)

We could remove a lot more than this, this is just a start.

There are various tools to help with this, knip is a good one

packages/twenty-server/src/modules/messaging/message-import-manager/drivers/gmail/types/gmail-message.ts

@@ -24,7 +24,7 @@ export type ParticipantWithId = Participant & {
   id: string;
 };
 
-export type Attachment = {
+type Attachment = {
   id: string;
   filename: string;
   size: number;

packages/twenty-server/src/modules/messaging/message-import-manager/drivers/gmail/types/gmail-thread.ts

@@ -1,4 +0,0 @@
-export type GmailThread = {
-  id: string;
-  subject: string;
-};